The invention involves utilizing Geopressured-Geothermal energy for beneficial uses. Geopressured-Geothermal (GPGT) energy is contained in the reservoir brines of certain sedimentary basins, unlike geothermal energy which are associated with volcanic hot-rock. The GPGT reservoir brines are highly pressured and hot, with values ranging 1000 psi to 4000 psi flowing surface pressure with 250° F. to 500° F. brine temperatures. The brines are entrained with natural gas, varying 20 to 100 scf/bbl. The brines can be recovered via well-bores, at high flow rates ranging 15,000 to 40,000 bbl/day. The available energies are: (1) the mechanical energy of the high pressure flowing brine; (2) the thermal energy via heat exchange with the hot brine; and (3) the chemical energy of the natural gas which can be withdrawn from the brine in a gas separator. The GPGT brines' water and salts are additional resources. The amount of salts and minerals dissolved in the GPGT reservoir brines, or Total Dissolved Solids (TDS), varies over a wide range: 3500 to 200,000 mg/l. The TDS are comprised of mostly Sodium Chloride, with lesser amounts of Calcium, Potassium, and other trace elements.
Generally there is an inverse relationship between brine TDS and brine gas content as the solubility of gas in water decreases with increasing salinity. There are at least seven known GPGT basins in the U.S. and about 60 others worldwide (Dorfman, 1988). The largest U.S. GPGT basin is in the Gulf Coast region with the second largest in the Central Valley of California. The U.S. Department of Energy (DOE) initiated the Geopressured-Geothermal Research Program in 1974 to define the magnitude and recoverability of GPGT energy in the U.S. Under this program, five deep GPGT research wells were flow tested in the Texas-Louisiana Gulf Coast region from 1979 to 1992. These flow tests demonstrated GPGT reservoir production longevity, ranging 5 to 7 years at sustained flow rates of 20,000 to 40,000 bpd (Negus-de Wys, et al, 1990; Riney, 1991; Riney, 1993). The specifics of the GPGT reservoir drive mechanism(s) have been debated (e.g., fault-enhanced fluid communication, shale dewatering, etc.) but it's widely accepted that the GPGT basins have outperformed conventional reservoir models (Ramsthaler, et al, 1988; Riney, 1988; John, 1989). The DOE ended funding for the GPGT program in 1992 and the last of the DOE test wells was plugged in December, 1993 (Rinehart, 1994).
The production of electricity from GPGT brine energy (i.e., flowing GPGT brine from a well-bore to recover/convert the kinetic, thermal, and gas energy) has been proposed by others (see example references from the Proceedings from the Industrial Consortium for the Utilization of the Geopressured-Geothermal Resource, Idaho National Engineering Laboratory, 1990-1991; e.g., the U.S. DOE demonstration at the Pleasant Bayou No. 2 GPGT test well, 1979-1992, Brazoria County, Texas, where a hybrid system at the GPGT well-head was used to generate electricity). Projects are currently being proposed and initiated to convert GPGT brine energy to electricity, and some have received funding from DOE Grants (e.g., see conference presentations related to Geothermal Energy Utilization Associated with Oil & Gas Development from the SMU Geothermal Lab).
The invention disclosed herein does not claim uniqueness regarding the particular GPGT-to-electricity process but rather shows unique novelty for the integration of those processes with a system, which incorporates certain methods from U.S. Pat. Re. 36,282 (Nitschke, 1999) along with new modifications, that allows for the concentration and use of the waste GPGT end-brine. All of the to-date proposals for converting GPGT-to-electricity have yet to find a suitable use for the massive volumes of thermally spent, de-gassed GPGT end-brine (e.g., approximately 5000-6000 bpd per MWe for a Frio type GPGT reservoir), and ultimately dispose these large quantities of raw GPGT brine, e.g., in downhole reservoirs, often at great expense, environmental impacts, and long-term risks. The invention disclosed herein integrates with existing GPGT-to-electricity systems and utilizes the GPGT end-brine for beneficial purposes (e.g., as construction material for salinity gradient solar ponds (SGSP), which are shallow, salt-gradient ponds that collect, store, and deliver baseload solar thermal energy for electricity production, sea water desalination, process heat, etc.), thereby greatly enhancing the overall economics of the GPGT-to-electricity project while also establishing renewable energy capacity, i.e., the SGSP systems.
The multi-effect distillation (MED) technology used in this invention is widely found and also discussed in U.S. Pat. Re. 36,282 (Nitschke, 1999) and in a subsequent filing by Nitschke (August, 2007) entitled “Enhanced Oil Recovery System for use With a Geopressured-Geothermal Conversion System”, which references' citations provide background for the MED technology. In U.S. Pat. Re. 36,282, Nitschke teaches producing GPGT brines through a well bore, flowing the brine to a hydraulic turbine for power generation, separating the gas, and then routing the brine to an MED unit for separating the GPGT source brine into saturated brine and distilled water end-products. In U.S. Pat. Re. 36,282, Nitschke further teaches utilizing the saturated brine end-product for the large scale construction of solar ponds.
Concerning spray evaporation technology related to the instant invention, salt recovery from sea water or brines via salt ponding, evaporation ponds for such purpose are an established practice. Typically, shallow ponds are filled with sea water and then the water is allowed to evaporate leaving behind solid sea salts that can be harvested. Spray evaporation ponds (SEP) utilize pump driven discharge nozzles exhausting over the pond surface to increase the surface area available for evaporative mass transfer; the driving potential for the mass transfer process is the difference between the vapor pressure of the discharging fluid and the water vapor pressure in the local air. Likewise, SEPs are in wide use for cooling, say, for heat rejection from power plants, although cooling towers are generally the preferred practice. Spray evaporation pond technology is also discussed by Nitschke in the subsequent August, 2007 filing (“Enhanced Oil Recovery System for use With a Geopressured-Geothermal Conversion System”). The invention disclosed herein is unique in its method of thermally charging the SEP via waste heat from a brine distillation process (i.e., per Nitschke, 2007) in combination with reject heat from power cycles utilizing GPGT brines, for the dual purpose of partially concentrating/conditioning the SEP brine waters for end-use while providing a power cycle heat-sink.
This information is noted here to the greatest import to underscore the potential, and national importance, of the invention's impact on the U.S. energy policy and portfolio, e.g., improving the economics of GPGT energy recovery and conversion, thereby enhancing the access and use of that major domestic energy resource, will help offset U.S. dependence on foreign oil (per USGS Circular 790, there are 5,700 quads of recoverable gas and 11,000 quads of available thermal energy in the Gulf Coast GPGT basin alone; U.S. total annual energy consumption is approximately 100 quads). Additionally, the method proposed herein provides for the efficient management of the GPGT brine end-salt, i.e., using it for cost-effective construction of SGSPs for large-scale production of solar thermal (baseload) energy, the lack of which (proper management of the end-salt) would inhibit full recovery of the GPGT potential. Lastly, the solar thermal renewable energy (e.g., baseload electricity) from the SGSP systems, installed via the GPGT conversion process of the present invention, approaches ˜10× of that energy produced by the GPGT-electricity systems themselves, hence having the potential to provide a major portion of our nation's renewable energy portfolio.
The inventor believes the known prior art taken alone or in combination neither anticipate or render obvious the present invention. Reference to the foregoing materials does not constitute an admission that such disclosures are relevant or material to the present claims. Rather, such materials relate only to the general field of the disclosure and are cited as constituting the closest art of which the inventor is aware.